Steer Emission Strength of an Shader by the position of an unrelated bone...how?
You can set a driver to a value node
Right click on your value node and choose add driver
then just choose transform channel if not as default and select your object/axis  



in the expression field you can do some operations to change/map you values
if you want it 1:1 then just put in the variable name, in this case "var"